Intravenous drugs are commonly administered utilizing injection through a self-sealing port, including y-adapters and prn adapters (also called saline wells or heparin wells). These intravenous systems commonly include deadspace which must be flushed free of the injected drug after the drug injection so that drug incompatibility will not occur with sequential injections of different drugs. Drugs are commonly injected in solution utilizing a conventional syringe with a needle or blunt cannula attached to the end for injection through the port. After the injection, however, a second syringe filled with saline must be inserted through the port to flush any residual drug solution from the deadspace of the tubing so that residual drug solution does not remain in this deadspace to prevent the potential for drug incompatibility should another drug be injected in the future through this same port. The nurse, therefore, draws up the drug with its solution into a first syringe and draws saline into a second syringe. The nurse commonly injects the drug solution through the port and into the patient, then injects the saline through the port to flush the drug from the deadspace of the system. Because sharp needles have been associated with significant infection risk to hospital personnel, it is common to utilize blunt or protected cannulas to provide safety during such injections. Since, as discussed, two injections are required to assure that the drug does not remain within the deadspace, the nurse must commonly utilize two separate syringes and two separate cannulas, resulting in considerable expense. Furthermore, multiple injections increase the risk of infection to the patient and, since such ports are commonly connected closely with an indwelling catheter, the greater the number of such injections, the greater the potential for manipulation of the catheter, which can result in thrombosis of the vein. In addition, multiple injections result in increase in exposure of hospital personnel to potentially infectious liquids from the patient and increase the amount of time spent in delivering drugs to the patient.
Given the aforementioned problems, there has long been a need for a system which can allow the nurse to inject a drug solution and subsequently flush the deadspace of the tubing or catheter utilizing the same syringe, thereby eliminating the need for multiple entries into the port and its associated problems.
An additional problem exists with automatic infusion devices which utilize syringes. These devices are commonly used for injection of medication into patients and do not require close attention by hospital personnel. However, once the infusion of these devices is complete, the drug may remain within the patient's vein and the deadspace of the tubing if the hospital personnel do not promptly arrive to flush the drug from these areas with saline solution. This can result in potential injury to the patient's vein, thrombosis, precipitation of the drug within the tubing, or chemical incompatibility and precipitation if another nurse fails to recognize the presence of drug within the tubing and injects a different incompatible drug into the tubing system. There is, therefore, a need for a system which can automatically flush the tubing after an injection whether or not the injection is provided by the nurse or a mechanical or electronic infusion device. This would allow more safe unattended injection by mechanical devices in the home setting. U.S. Pat. No. 4,857,056 describes a system for providing automatic infusion of a drug followed by a flush solution. This device, however, requires the provision of two syringes and many mechanical and electronic infusion devices are designed to interface with a single syringe. Furthermore, two syringes result in additional expense when compared with a single syringe system.
As hospital costs increase, it has become desirable to reuse disposable medical equipment for the same patient for short periods of time (for example, 24-96 hours). It is, therefore, advantageous to provide a multiple use syringe for use with a single patient over multiple aspirations and injections of sequential medications. U.S. Pat. No. 4,439,184 discloses a single syringe for the injection of two different drugs. The syringe has proximal and distal chambers and two pistons and a proximal no-pass region and a distal by-pass region. However, this syringe can only provide a single sequential injection from each compartment since there is no provision for withdrawing the distal piston from the by-pass region for sequential fluid withdrawal or for presetting the volume of the proximal chamber during the withdrawal maneuver. Therefore, there is no provision for allowing the nurse to easily aspirate the respective solutions into the syringe. There are numerous additional multi-chambered syringes in the prior art: U.S. Pat. No. 5,102,388 discusses a multi-chamber syringe for sequential injection of different drug solutions. Piercing devices are disclosed which sequentially pierce stoppers during the injection; U.S. Pat. No. 5,125,892 discloses a multi-chambered syringe having a hollowed dilated piston which can burst; U.S. Pat. No. 4,655,747 discloses a dual-chambered syringe having an inner and outer barrel; U.S. Pat. No. 4,610,666 discloses a tandem barrel syringe; U.S. Pat. No. 4,496,344 discloses a multiple compartment syringe having a distal bypass region; U.S. Pat. No. 4,464,174 discloses a two-compartment mixing syringe with an inner and outer barrel; U.S. Pat. No. 4,453,934 discloses a piston having a distal container which can fracture for the sequential delivery of, for example, a contrast agent followed by a saline flush solution; U.S. Pat. No. 3,985,122 discloses a syringe having two bores and two pistons having different diameters for mixing solutions within the syringe; U.S. Pat. No. 3,807,199 discloses a method for assembling a multiple compartment syringe and for preloading the syringe with a measured quantity of liquid; U.S. Pat. No. 3,494,359 discloses a two-compartment syringe utilizing a compartment separator which can deflect for mixing of the solution; U.S. Pat. No. 3,511,239 discloses a two-compartment syringe having two pistons and a rod extending through the pistons with a longitudinal bore which provides communication between the two chambers, allowing the fluid in the upper chamber to be mixed with the drug in the lower chamber; U.S. Pat. No. 4,792,329 describes a mixing syringe having a bypass region and three separate stoppers for mixing and subsequently injecting two solutions; U.S. Pat. No. 4,693,706 describes a mixing syringe having inner and outer cylindrical barrels for mixing two solutions; U.S. Pat. No. 4,834,714 describes a double barrel arrangement capable of achieving the double capacity of a single syringe; U.S. Pat. No. 3,680,558 discloses a multiple compartment syringe having telescoping barrels with an intermediate valve which can be opened by rotation; PCT Application WO92/01485 discloses a syringe having a barrel with a cylindrical insert for long-term storage and subsequent mixing and injection of two drugs. In addition to the foregoing discussion, the above patents provide additional general background of this invention. Importantly, multi-barrel syringes are associated with additional expense and complexity whether in tandem or telescopic configuration. Also, it is expensive to preload a multi-compartment syringe with flush solution and pre-loading may require the addition of glass or other containers to maintain stability of the solution, which adds additional expense. To achieve reduction in cost, it would be advantageous for the nurse to aspirate a specific preset quantity of flush solution into the syringe immediately prior to use. It would further be advantageous for the volume of this flush solution to be preset by an indicator so that the nurse is confident that adequate flush volume is present to completely flush the deadspace of the syringe and the deadspace of conventional wells when it has been indicated by the indicating means that the syringe contains adequate flush volume. The present invention functions to achieve these and other advantages, as will become evident from the following discussion and claims.
Another common problem relates to blood sampling. Syringes have been commonly used to draw blood out of intravenous lines or arterial lines. However, such blood is commonly diluted with the saline or heparin solution which generally dwells within the deadspace of the intravenous or arterial line. Problems related to blood collection are described in U.S. Pat. No. 3,835,835, which discloses a multi-barrel two-compartment syringe for collecting a pure uncontaminated blood specimen. Another system for isolating pure blood is discussed in my U.S. Pat. No. 4,838,855 (the disclosure of which is hereby incorporated by reference as if completely disclosed herein). This patent describes a system and method for repetitively achieving an undiluted specimen of blood outside a patient for testing or sampling. The system utilizes a variable volume reservoir and predetermined volumes to separate the fluid which is indwelling within the tubing system from the blood and fluid mixture that naturally occurs upon withdrawal of blood into the tubing. This allows the stored fluid within the syringe which is not contaminated with blood to be utilized to flush blood from the system after blood testing or sampling. This system has the important advantage of providing for the separation and isolation of a portion of the original fluid stored within the deadspace of the tubing from the blood that is withdrawn into the system so that the isolated fluid can later be used to flush the blood from the tubing, thereby providing ease of operation and reducing the risk of accumulation of blood within the deadspace of the reservoir. The system also minimizes the amount of total fluid added to the system and the patient during repetitive sampling or testing.
Commonly, however, it is necessary to draw blood at substantial distances from the indwelling catheter, such as during anesthesia when the anesthesiologist is sitting at the head of the bed above the head of the patient and wherein the patient is draped by sterile drapes for surgery. A radial artery catheter is positioned in an arm, which often is directed downward at the side of the patient. Therefore, the anesthesiologist is required to sample blood at the head of the bed from an arm positioned near the patient's hip so that the distance may be substantially greater than 1 meter. In such situations, it would advantageous to store the blood and fluid mixture within a syringe reservoir, rather than solely within the tubing itself, since the length of the tubing is so great between the patient and the sampling site that a large volume of blood must be drawn into the system to adequately clear the line at the sampling site. Furthermore, it is commonly necessary to draw blood from indwelling catheters that do not have fixed reservoirs attached, such as multilumen catheters. Such catheters commonly do not conventionally have adequate tubing length to provide the capacitance storage function described in my aforementioned patent.
In addition to these problems, it would be advantageous not to leave certain toxic drugs or radioactive materials within the deadspace of a syringe or cannula or heparin well after an injection. This is particularly true with the injection of chemotherapeutic drugs which may be highly toxic to the nurse providing the injection if the nurse is exposed to even minute quantities of the drug over a sustained period of time. An injection of a chemotherapeutic agent through a cannula and then the withdrawal of that cannula can result in minute quantities of the chemotherapeutic agent being expelled in the region around the injection sight or in the environment prior to dropping the cannula and/or syringe within the waste receptacle. This is also true of radioactive materials which are commonly injected (for example, during an exercise stress test) at a time wherein minute quantities are best completely injected into the patient so that there is less potential exposure of hospital personnel to residual radioactive material outside the patient within the deadspace of the cannula or syringe. Although the volume is small, leaving drugs or radioactive material in the deadspace is also wasteful when considered collectively throughout the year in a large hospital.
The present invention functions to specifically, allow the aspiration of a capacitance storage volume of a flush volume, which can later be used to flush the deadspace of the reservoir and the deadspace of a tubing system and catheter. This invention is usable in many medical environments, including the administration of drugs wherein deadspace drug must be flushed from the system and the collection of blood wherein the flush solution must be isolated from undiluted blood to provide a pure blood sample or where the deadspace of the syringe must be flushed free of blood for repetitive fixed reuse with indwelling catheters.
The sequential aspiration syringe comprises a variable volume chamber, such as a syringe barrel or cylinder having an opening which can include a conduit adjacent the distal end for flowing liquid into and out of the chamber. The injection system further includes a volume adjuster, such as a piston with a handle for adjusting the volume within the variable volume chamber. The syringe further includes a chamber divider, which can be a second piston that is positioned within the chamber. The volume adjuster is linked to the divider by a connector or tensile element such as a tether. The tensile element is preferably flexible and collapsible, and preferably filamentous. The chamber divider effectively divides the chamber into two variable volume reservoirs, a proximal or upper primary reservoir and a distal or lower secondary reservoir. The syringe further includes a flow channel which may be in a fixed position along the barrel adjacent the distal end or which may be moveable and carried by the divider piston, or which may be dynamically formed by a positionally-derived flow space or separation between the divider piston and at least a portion of barrel wall when the divider piston is positioned adjacent the distal end. The syringe further includes a valve which enables fluid to pass through the flow channel around or through the chamber divider to pass between the secondary reservoir and the primary reservoir. The valve can be the divider piston or can be located within or otherwise carried by the divider piston. The flow channel preferably provides for bi-directional flow between reservoirs. In one preferred embodiment, the passage of fluid through the flow channel can be enabled or disabled by positioning the chamber divider at different positions along the chamber. In one preferred embodiment, flow through the flow channel is disabled by traction on the tensile element and flow is enabled by contact between the divider and the distal end of the barrel. The positionally selective enablement and disablement of the venting of fluid about the chamber divider provides a mechanism for the preset selective adjustment of maximum volume of aspirated fluid within either the secondary reservoir or the primary reservoir, and for the sequential administration of this fluid from the secondary reservoir and the primary reservoir. In the preferred embodiment, the primary reservoir has a fixed maximum volume. The primary and primary reservoirs are in fluid connection with the conduit connected to the distal end of the chamber so that fluid may flow from either reservoir through the conduit and out of the injection system.
The stop for stopping the divider piston face from pressing against the tapered end and thereby trapping fluid between the face and the tapered end can be positioned upon the face of the divider piston, along the bore, or can comprise complimentary detents for engaging the handle or the main piston and thereby preventing further advancing force of the handle and main piston against the divider piston.
The main piston can reduce pressure within the upper primary reservoir, and the tensile element can selectively lower the pressure in the secondary reservoir when the tensile element is extended and the primary reservoir has been filled. The tensile element can provide for equivalent retraction of the main piston and the divider piston when the primary reservoir has been filled to prevent lowering pressure within the primary reservoir even with further retraction on the main piston so that substantial fluid flow into the primary reservoir would be inhibited even without a valve which disables flow between the reservoirs after primary reservoir filling.
In operation, prior to use, both reservoirs are preferably empty. Initially, there is fluid communication between the secondary reservoir and the primary reservoir. The divider is preferably positioned so that the secondary reservoir has very little or no internal volume. In operation, the distal conduit is connected to a source of fluid such as a blood line or the distal conduit is connected to a cannula which is inserted into a saline flush vial or the like. The volume of the primary reservoir is then increased by the volume adjuster to cause flow of fluid into the distal conduit and then through the flow channel and into the primary reservoir. The flow through the flow channel is preferably enable by positioning the divider adjacent the distal end, which is the resting position of the divider prior to use. During this time, the divider is preferably restrained from moving, as by a detent, thereby preventing enlargement of the secondary reservoir and assuring the divider remains in the venting position despite the relative negative pressure within the primary reservoir. This also allows the nurse to freely turn the syringe upward to expel any aspirated air without effecting the contents of the secondary reservoir. When the primary reservoir is filled (usually with saline), the tensile element connecting the volume adjuster and the chamber divider becomes fully extended and pulls the chamber divider against the restraining detent. This provides tactile indication of completed filling of the primary reservoir, although other indicating means would also be effective. The nurse then can connect to a distal conduit to a second liquid source such as a drug vial. Further retraction then causes the divider to displace from the venting position. The tensile element is preferably strong, but of minimum fluid displacement volume, such as a nylon filament. Upon displacement, the flow channel is closed so that additional fluid does not pass into the primary reservoir. The volume of the secondary reservoir is then enlarged so that fluid passes through the distal conduit into the secondary reservoir until the secondary reservoir is adequately filled. Again, the nurse can turn the syringe upward after aspiration and expel any aspirated air from the secondary reservoir without effecting the contents of the primary reservoir. At this time, the flow channel which previously provided fluid communication between the primary reservoir and the distal conduit is closed so that fluid cannot flow from the distal conduit into the primary reservoir. Furthermore, the secondary reservoir is isolated from the primary reservoir so that mixing of the fluids between the reservoirs cannot occur. Once both reservoirs have been adequately filled the container now includes two sequentially stored volumes of fluid which are isolated one from another and which may contain distinctly different solutions. When injection is desired, each volume of fluid can now be forced in a sequential fashion back through the distal conduit in the reverse order in which they were stored. To inject the fluid, the volume adjuster is advanced, thereby increasing the pressure within the primary reservoir which is transmitted to the secondary reservoir. When the pressure within the secondary reservoir is increased, fluid can move from the secondary reservoir into the distal conduit. However, during this time, the flow connection between the distal conduit and the primary reservoir is disabled so that flow cannot move from the primary reservoir to the distal conduit even if pressure is increased within the primary reservoir. With advancement of the volume adjuster, the primary reservoir moves along the chamber while maintaining a constant volume, the hydraulic force of the trapped liquid causing the divider to advance. Once the secondary reservoir has emptied, the flow between the primary reservoir and the distal conduit is enabled. The enablement is preferably induced when the divider enters the venting region adjacent the distal end of the chamber and may be activated by contact with the distal end of the chamber. Means to indicate enablement of vented flow can be included such as a marker located at a position of the handle or a detent. When the divider is in this position, flow can occur between the primary reservoir and the distal conduit. During this time, as the primary reservoir empties, the tensile element collapses, coils, or folds such that the movement of the volume adjuster toward the divider is preferably not inhibited. In this way, it can be seen that at least two different fluids may be sequentially withdrawn into and stored within the chamber and isolated one from the other by first withdrawing fluid in the primary reservoir and then withdrawing a different fluid into the secondary reservoir. These fluids may then be injected sequentially in the reverse order of aspiration, first from the secondary reservoir and then from the primary reservoir. The fluid from the primary reservoir is preferably circumferentially expelled through the deadspace of the secondary reservoir and conduit to allow a complete flush of the system and the volume of the primary reservoir can be preset to assure a complete flush of the secondary reservoir and conduit. Also, this sequential aspiration and injection preferably occurs through the same distal conduit so that there is no need to disconnect and reconnect for sequential aspiration and/or injection of fluids. It can be seen that when the flow channel is not in fluid connection with the primary reservoir that the primary reservoir and the two pistons represent a single retractable piston assembly with a proximal and distal portion separated by the primary reservoir and with a fixed internal volume and with a fixed piston assembly length, as defined by the tether element. The piston assembly can move along the barrel and the piston assembly can collapse to shorten in length when the fluid escapes from the primary reservoir and can enlarge in length when fluid enters the primary reservoir, both shortening and lengthening occurring to movement of the proximal portion toward or away from the distal portion.
An example of use is with blood sampling, wherein fluid without blood admixture can be stored in the primary reservoir and blood and fluid mixture can be stored in the secondary reservoir. Alternatively, for the administration of drug solutions, it can be seen that saline can be initially drawn into the primary reservoir and the drug solution drawn into the secondary reservoir. When the distal end of the distal conduit is then connected to an intravenous line of a patient, the reservoirs are emptied in the reverse order in which they were filled such that the drug solution is injected into the patient followed by the injection of saline. All of this can be achieved with much greater simplicity since disconnection and reconnection of multiple syringes are no longer necessary when utilizing this device.
In another system embodiment for blood sampling, the syringe can be permanently attached a second conduit which is connected to a first conduit with an access port intermediate the first and second conduit. The first conduit is connected to a terminal of a conventional catheter, for example, a multilumen catheter. (These catheters often have a low internal fluid volume so that very little resident flush solution is available within the catheter for filling the primary reservoir.) The first conduit of the system includes an access port which can be utilized for drawing a blood specimen or for infusing liquid. Indeed, an intravenous tubing could be connected to this access port so that liquid can continuously infuse through this port when a blood sample is not being obtained. The maximum displacement volume of the primary reservoir can be preset so that it is less than the internal fluid volume of the first conduit, the second conduit, and the internal fluid volume of the catheter. In this way, this volume can be preset so that, upon withdrawal of fluid into the syringe, only flush solution will enter the primary reservoir. The syringe can, therefore, can be used to draw fresh pure blood past the access port for sampling by insertion of a cannula through the access port. It is considered preferable to have a minimal deadspace intermediate the syringe and the access port so as to provide adequate saline flush of all residual blood from the deadspace with minimal flush volume. The system can be constructed such that substantial priming deadspace of resident flush solution is supplied with the first conduit intermediate the access port and the blood vessel. This assures that adequate flush volume is present so that the primary reservoir can aspirate a large enough flush volume to later provide an adequate flush of the primary conduit and the deadspace intermediate the syringe and the access port. In another embodiment, the access port is positioned adjacent the distal end of the syringe so that substantially no deadspace is present between the distal end of the syringe and the access port, thereby further minimizing the requirement for higher flush volumes. Whether the access port is placed without deadspace in juxtaposition with the syringe or whether the access port is connected by a low deadspace conduit will depend upon whether it is desirable to place the syringe directly upon the catheter or at some distance from it. In any case, the volume of the secondary conduit is preset during manufacture to be less than the internal fluid volume of the catheter and the conduit portions distal the syringe. Subsequent each blood aspiration maneuver, some blood mixed with fluid will remain within the first conduit or catheter and this can be easily flushed by inserting a cannula into the access means and flushing saline through the access means. Also, with this system, any source of fluid which is connected to the second conduit or otherwise proximal the access means could effectively flush any residual blood distal the access means after each blood withdrawal maneuver.
It is, therefore, the purpose of this invention to provide an apparatus and method that will eliminate the need for multiple syringes for the administration of drugs through IV systems. It is further the purpose of this invention to provide a simplified method and apparatus for the sampling of blood from an indwelling catheter within a patient's blood vessel which does not require the use of a first syringe to withdraw and discard the resident portion of fluid within the catheter and associated tubing system. It is further the purpose of this invention to provide a system for withdrawing blood into a syringe and flushing the blood back out of a syringe utilizing reciprocating saline volumes with minimal additional volume administration to the patient and further simplifying the process of syringe flushing, as for repetitive undiluted blood isolation within arterial lines for sampling or ex vivo testing. It is further the purpose of this invention to provide an inexpensive device which allows blood collection and drug administration with a single unified apparatus, thereby reducing overall cost of manufacture. It is further the purpose of this invention to provide an inexpensive blood collection and drug administration system which utilizes a novel, simple method of sequential withdrawal of liquid followed by sequential injection in the reverse order of the withdrawal, which method simulates conventional single syringe aspiration and injection, thereby providing greater ease of use for nursing personnel. It is further the purpose of this invention to provide an apparatus having an inexpensive means, such as a filamentous tensile element, for adjusting the maximum volume within the primary reservoir during manufacture so that a wide range of such devices having different maximum volumes can be manufactured for different applications without substantial increase in manufacturing cost. It is further the purpose of this invention to provide a single unified apparatus and method for the compartmentalization and isolation of two different fluids within a single syringe utilizing a single withdrawal maneuver and to allow the nurse to expel aspirated air from either compartment during each withdrawal process and to provide the subsequent sequential injection of these two different fluids utilizing a single injection maneuver. It is further the purpose of this invention to provide a multiple reservoir syringe which includes a bi-directional, positionally-enabled, circumferentially-directed flushing and aspirating mechanism which freely vents a high flow of fluid from a primary reservoir upon completed injection of liquid from a secondary reservoir to completely flush the secondary reservoir free of blood or drug solution with a minimum volume of fluid. It is further the purpose of this invention to provide and inexpensive system for connecting, within a syringe sequential pistons with a tensile element of low fluid displacement volume and high flexibility to allow delayed distal piston retraction at a predetermined volume during proximal piston withdrawal and subsequent uninhibited proximal piston advancement toward the distal piston to achieve a simplified method of sequential aspiration and flushing and so that the internal volume of the syringe is not significantly effected by the displacement volume of the element. It is further the purpose of the invention to provide a mechanism for disabling flow between a proximal and a distal reservoir which is activated at a specific filling volume of the primary reservoir and which is activated by retraction of a tensile element. It is further the purpose of this invention to provide an automatic flushing syringe which can be used with automatic, electronic, or mechanical injection systems for unattended injection and subsequent flush into a patient with a single syringe. These and other objects and advantages of the invention will be further set forth in the description which follows and, in part, will be learned from the description or may be learned by practice of the invention. The objects and advantages of the invention may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims.